jgs1564

I’ve had my 2018 E400 Coupe for almost two years now. For the first 20 months, the engine auto start/stop feature was working flawlessly. It would shut the engine off almost every time I came to a stop. For the past 3 or so months, it’s has slowly quit working properly. When I start driving in the morning, it works just fine and shuts off the engine every time I come to a stop. After about 2 hours (not of continuous driving), it quits working completely. It doesn’t matter if I’m making short trips in the car, or longer trips. It will work great for the first couple of hours and then it stops working completely for the rest of the day. After parking the car overnight, it will start working properly again the next morning for the first couple of hours and then quit again. This pattern is consistent regardless of how long, or how often I drive the car each day. I’m retired, so I don’t have a regular daily commute. My trip cycles vary from short trips to the store/gas station/etc, to longer trips of 1 hour or longer.

I’ve taken the car to my local MB dealership twice for this issue. The first time, they determined that the battery that is connected to the start/stop feature needed to be replaced. After they replaced the battery, the feature worked perfectly for 3 days and then went back to the same problem. I took the car in a second time and they said it was working fine. They kept the car overnight (both times). Both times, I was put in loaner cars. I noticed that the start/stop feature in both loaner cars worked properly - it didn’t matter what time of the day or evening I drove the car, or for how long. The service advisor said that the feature on my car is designed to disengage when the car’s engine reaches higher temperatures. If that is the case, why did it work perfectly for the first 20 months I had the car? Also, why did the feature on both loaner cars work properly? I’m not buying his explanation for one minute.

Any suggestions on what I can do. I’ve thought about taking my car to another dealership, but not sure if I want to go through the hassle. Also, the next nearest dealership is a good 30 minutes away from my house.

Any suggestions and/or feedback is greatly appreciated.

whoover

Mine is sensitive to battery charge. A new AGM battery will not be as fully charged as it is capable of, and the car's electrical system will not charge it long enough to take it to its saturation voltage either. I found that a good AGM charger needed 48 hours to declare the battery fully charged, and that made a big difference in the stop/start function. This is the charger I use:

The other thing to note is that hot weather will affect it, but not as described by your SA. It's about the air conditioner. If the climate control needs the AC compressor running, it will override the autostop. You can determine if that's happening by cranking up the temp as a test. But considering you had a bad battery and now have a new one, I'd definitely try hanging an AGM charger on it until the voltage tops out.

jgs1564

Thank you for the information regarding the AGM charger. I will mention this to the dealer the next time there and see what they say.

whoover

If they try to sell you the MB-branded one for twice as much, resist. It's also made by CTEK but is an older model. If they give you a song and a dance about only the MB one being safe, resist it. The one I linked has an AGM-only mode and does a much better job (more sophisticated charging cycle).

pdeacon

I wish mine would stop working. Then I wouldn't have to turn it off every time I start the car.

BenzC400

I generally keep my ECO start/stop system off. The E53 with the Integrated Starter=Generator (ISG) and 48 volt electrical system has a very good ECO start/stop system. It’s the most unobtrusive system I’ve tried so far. Even so, there is some delay when starting up. I still prefer to turn it off each time I start the car. The only time I intentionally use the system is when I’m parked and waiting in the car. The 48 volt electrical system allows the cars systems, including the airconditioning, to remain on for an extended period, even with the engine off.

DFW_Neal

I have a 2019 E53 Cab and it activates sometime and not others. It only works in E or C mode. Much more consistently in E mode. I find that if I want the engine to stop at a red light if I press the brake and activate the “Hold” feature the engine will turn off. But I mostly drive in Sport mode so a non-issue.

BenzC400

I’ve noticed that in the E53 the ECO start-stop only activates in C and E modes, however the green “on” light stays lit even in S and S+ modes. In my former C400, the ECO start stop on light went off in S and S+ modes.

whoover

Same in the E63. (No E mode, but ECO works only in I or C even though the light is on in S, S+ or R.) It sort of makes sense because the button is a global setting. In other words, if you turn it off it stays off if you move to S and then back to C. If the light were mode-dependent it would be ambiguous. (If you turned it off in C, switched to S and then back to C should it come on again, reflecting the mode setting, or stay off, reflecting the global setting.)